Microsensor housing

Abstract

A microsensor housing having a structure with at least one inlet at one end and a thermal property sensor at the other end. Situated between the inlet and the sensor is a convection shield. Sampled fluid is taken in the inlet from a channel carrying the fluid to be sampled. The convection flow lines of the fluid are barred by the convection shield. The fluid is diffused into a cavity between the shield and sensor. The sensor detects a thermal property of the diffused fluid. One preferred shield has holes about its perimeter with a solid center part of the shield covering at a distance the sensor. The channel carrying the fluid may have screens to reduce turbulence noise and to aid in fluid transport to and from the sensor housing.

What is claimed is:  
     
       1. A sensor and sensor housing assembly comprising: 
       means for sensing at least one thermal property of a fluid, said means for sensing including a heating element and a sensing element arranged in a microbridge configuration;  
       means for shielding, proximate to said means for sensing, for shielding said means for sensing from convection of the fluid that detrimentally affects an accuracy of the sensing the at least one thermal property of the fluid, said means for shielding including a plurality of concentrically spaced holes; and  
       means for reducing velocity and conveying a portion of fluid to said means for shielding.  
     
     
       2. The sensor and sensor housing assembly of  claim 1 , wherein: 
       said means for shielding is situated more than 50 microns from said means for sensing.  
     
     
       3. The sensor and sensor housing assembly of  claim 2 , wherein said means for sensing is supported on a surface on the sensor housing assembly, and said means for sensing comprises: 
       a substrate situated on the surface supporting said microsensor means;  
       a semiconductor piece formed on the substrate, the semiconductor piece including a recess; and  
       a thermal sensing element proximate to the recess.  
     
     
       4. The sensor and sensor housing assembly of  claim 3 , wherein the sensing element is situated in a membrane covering the recess. 
     
     
       5. The sensor and sensor housing assembly of  claim 4 , wherein the recess contains a thermally isolating material. 
     
     
       6. The sensor and sensor housing assembly of  claim 5  wherein: 
       said means for reducing velocity has a first end proximate to said shield means and a second end;  
       the second end is an opening that has an area equivalent to a circle having a first diameter;  
       the second end is at a first distance from said shield means; and  
       a ratio of the first diameter to the first distance is close to or greater than one.  
     
     
       7. The sensor and sensor housing assembly of  claim 3 , wherein the recess is filled with a substance having a low thermal conduction. 
     
     
       8. The sensor and sensor housing assembly of  claim 1 , wherein said means for sensing is supported on a surface on the sensor housing assembly, and said means for sensing comprises: 
       a substrate situated on the surface supporting said microsensor means;  
       a semiconductor piece formed on the substrate;  
       the semiconductor piece including a recess; and  
       a thermal sensing element proximate to the recess.  
     
     
       9. The sensor and sensor housing assembly of  claim 8 , wherein the recess is filled with a substance having a low thermal conduction. 
     
     
       10. The sensor and sensor housing assembly of  claim 1  wherein: 
       said means for reducing velocity has a first end proximate to said shield means and a second end;  
       the second end is an opening that has an area equivalent to a circle having a first diameter;  
       the second end is at a first distance from said shield means; and  
       a ratio of the first diameter to the first distance is close to or greater than one.  
     
     
       11. The sensor and sensor housing assembly of  claim 10 , wherein the recess is filled with a substance having a low thermal conduction.